MODULAR POWER PLANT FOR THE GENERATION OF ELECTRICAL ENERGY FROM SOLAR ENERGY

Abstract: A modular power plant for the generation of electrical energy from solar energy. The principle structure consists of: a conversion module (1) for the conversion of solar energy into biological raw material, a gasification module (2) in form of a gasification reactor for the gasification of biological raw material, and a fuel cell module (3) for the conversion of gas into electricity using fuel cell technology. The conversion module (1) contains an aggregate (4) for harvesting biological raw material and a processing aggregate (5) for processing biological raw material into a gasification preproduct. The gasification module (2) is connected to the processing aggregate (5) via a supply unit (6). The fuel cell module is connected to the gasification module for cleaning of the fuel gas by a device (8). The performance of the gasification and fuel cell module has been designed in relation to the system performance, so that part of the fuel gas can be used for the water vapour production (12) and a further part and/or the waste heat of the modular power plant for the drying of harvested biological raw material.

Description: Modular Power Plant for the generation of electrical energy from solar energy. Description The invention refers to a Modular Power Plant for the gen¬ eration of electrical energy from solar energy. Modular Power Plant means, that the Power Plant consists of several modules with different functions, of which the Power Plant as a whole is constructed. The modules are made in serial production. It is understood, that modules are connected by functional and control lines. A Modular Power Plant for the provision of mainly hydrogen from solar energy is unknown. However, Solar Power Plants consisting of several similar modules, so called sun col¬ lectors, for the absorption of solar energy are known, in which a thermal effect aided by thermal heat engines or a photoelectric effect, converts solar into electrical en¬ ergy. Furthermore Power Plants containing at least one gasification reactor for the gasification of fossil fuel and biological raw material into fuel gas are known, in which the fuel gas is converted into electricity by a ther¬ mal heat engine. Biological raw material generally refers to all regenera¬ tive raw material, i.e. such raw material which can be bio- logically restored depending on the vegetation cycle of a region. Biological raw material differs therefore from fos¬ sil fuel which takes considerably longer to form than to be used. Biological material can principally be provided with intact cell structure or disintegrated structure, i.e. as fine powder. The main elements contained in biological raw material are carbon, hydrogen, oxygen and nitrogen with little protein and sulphur. With regards to the invention, biological raw material refers to fast growing plants, es¬ pecially perennial plants and plants high in lignin. Bio¬ logical raw material in this context refers to preferably C-plants, C-reeds and C 4 -grass. The protein and sulphur contents can be influenced by fertilisation. Furthermore the direct generation of electricity from hy¬ drogen using fuel cells is well known and especially suited for a relatively low performance in the region of 1 to 5 MW. Compared to thermal heat engines, fuel cells have the advantage of not being subjected to the thermodynamic effi¬ ciency limitations of the Carnot cycle. Theoretically, fuel cells can achieve a near perfect conversion of combustion heat into electrical energy from the reaction of hydrogen and oxygen to water. In operation fuel cells can therefor easily attain considerably higher efficiencies than thermal heat engines. This, however, assumes that the catalysts are not poisoned by catalytic poison potentially contained in hydrogen. Molecular hydrogen is not available as raw material for the generation of electrical energy, but must be produced from hydrogen containing raw material. The generation of hydro¬ gen from water using normal electrolysis uses more elec- tricity than is generated by the hydrogen and is therefore not a feasible option. The catalytic water fission in hy¬ drogen and oxygen is extremely slow and yields despite high expenditure only low quantities making it commercially un¬ attractive. The generation of so called synthetic gas from coal, prin¬ cipally containing hydrogen and carbon monoxide and the systems required for this process, have been known for some time, the process being called coal gasification. In a so called water shift reaction, the carbon monoxide of the synthetic gas can be converted into hydrogen and carbon di- oxide by adding water vapour and applying heat. In principal synthetic gas can be used for the operation of fuel cells although in operation this has shown consider¬ able disadvantages. Firstly coal normally contains raw ma- terial sulphur being dragged along as gaseous sulphur com¬ pound in synthetic gas. Sulphur compounds, however, are normally strong .catalytic poisons which . can irreversibly deactivate the catalyst of a fuel cell and consequently the fuel cell itself. From an environmental aspect sulphur gases are also an undesired emission. Secondly the overall generation of synthetic gas from coal is extremely expen¬ sive and difficult as costs from underground mining, coal gasification and required desulphurization accumulate. Until today electrical energy is produced centrally in large Power Plants although the power usage of individual local users is comparatively small. The underlying technical problem of the invention is the easy local conversion of solar energy into electrical en¬ ergy. The. technical problem is solved by the invention of a Modular Power Plant for the generation of electrical energy from solar energy, in which a) a conversion module for the conversion of solar en¬ ergy into biological raw material, being suffi¬ ciently free from raw material sulphur, in form of an agricultural area cultivated with plants, espe¬ cially C 4 -plantS / is convertible into biological raw material. b) a gasification module in form of a gasification re¬ actor gasifies biological raw material into a fuel gas using water vapour and increased temperatures, in which the gasified products remain in the gasi¬ fication zone of the gasification reactor for a certain period, to suppress tar condensation in zones after the gasification zone of the gasifica¬ tion module and/or a subsequent fuel cell module. c) a fuel cell module in which the fuel gas is con- verted into electrical energy using fuel cell tech¬ nology, the conversion module being an aggregate for harvesting biological raw material and a processing aggregate for the processing of biological raw material into a gasification preproduct, the gasification module being connected -to the processing aggregate by means of a supply unit, the fuel cell module being connected to the gasification module for the cleaning of the fuel gas by a device, the performance of the gasification and fuel cell module matching each other in relation to the system performance and in such a way, that part of the fuel gas can be utilised for water vapour generation and a further part and/or waste heat of the Modular Power Plant can be utilised for the drying of harvested biological raw material, the size of the conver¬ sion module depending on the stipulated system performance in relation to the cultivated area, the conversion module containing a processing aggregate in form of at least one harvester for biological raw material and a chaff cutter or pelleter. Within the context of the invention the harvested biological raw material is bundled and/or bailed and stored to process the biological raw material into the gasifica¬ tion preproduct when required. Alternatively storage could be provided for the processed biological substance to bal¬ ance quantity variations of processed biological raw mate¬ rial caused by vegetation cycles. It is understood that as part of the invention several Modular Power Plants of the described structure can be installed next to one another, the conversion module also allowing the operation of sev¬ eral Modular Power Plants. The generated electrical energy can be used locally or fed into a grid. The principal ele- ents of the conversion, gasification and fuel cell module are preferably prefabricated as modular elements of a Modu¬ lar Power Plant, being transportable in an assembled and disassembled condition. The invention is based on the fact that solar energy can be absorbed and stored in considerable amounts with little technical effort within vegetation cycles of geographical zones using natural sun collectors i.e. plants being con¬ vertible into biological raw material. Solar energy stored in this way can be converted easily into electricity if the conversion into electricity takes place at the storage site, the combination of characteristics b) and c) is real¬ ized and modules for a Power Plant of relative low perform¬ ance i.e. 1 to 5 MW are installed at the storage place. For this the individual modules are produced centrally and transported to the storage place or split into further com¬ ponents for transportation. At the installation site the aforementioned performance matching of the conversion mod¬ ule to the performance supplied and stipulated for the gasification and fuel cell module takes place. In this re¬ spect the invention combines a natural conversion process for solar energy with hardware elements and the so formed conversion module with proven aggregates for the generation of fuel gas and conversion into electricity which are them¬ selves formed as modules. The invention offers various extension and design options. A preferred form of the invention is characterised in that the gasification module is set to allothermal gasification - and preferably operated with the fuel gas having a water vapour/biological substance proportion of larger than 1. The gasification module contains a gasification reactor be¬ ing pressurised and operated with water vapour as gasifica¬ tion and fluidising agent, as is usual for fossil fuels (see EP 0 329 673 Bl) . The invention also offers several options with regards to the fuel cell module.; The fuel cell module can for instance consist of at least one fuel cell with a phosphoric acid electrolyte. According to another option, the fuel cell module contains at least one fuel cell with a carbonate melt electrolyte. According to a further option, the fuel cell module contains at least one solid oxide fuel cell. An especially important suggestion of the invention is the provision of at least one proton exchange membrane in the fuel cell module. A preferred form of the invention distin- guished by guaranteed operation and long life of the mod¬ ules, especially the fuel cell module, is characterized by the combination of a gasification module set up for al- lother al gasification with a fuel cell module containing at least one fuel cell with a phosphoric acid electrolyte. Alternatively fuel cells can be combined in a fuel cell module according to claims 5 and/or 6 and/or 7 and/or 8. In all cases, however, module life is enhanced, if the gasi¬ fication module is adjusted to a oxygen/biological raw ma¬ terial proportion and a gas phase temperature, ensuring a near nitrogen oxide free fuel gas. Surprisingly a gasifica¬ tion module set up in this way does not produce harmful tar condensation, especially when the gasification itself is allothermal. A modular power plant according to the invention can oper¬ ate self-sufficiently with little effort. For this the in- vention stipulates an additional water vapour generating module being heated by part of the fuel gas. The conversion module can also be equipped with a drying unit heated by the waste heat of the Modular Power Plant. In a Modular Power Plant according to the invention, ash is produced by the gasification, which can be used as fertiliser for the conversion module. Plants and especially the perennial C 4 -plants, being convertible into biological raw material, die only after five, ten or more vegetation cycles. Only then the conversion module must be recultivated agricultur- ally. Below some of the fuel cells suitable for the fuel cell module of a Modular Power Plant of the invention and their integration into a gasification module are explained in more detail. According to one option of the invention the following pro¬ cedure is adopted: Biological raw material is utilized which due to for in- stance suitable fertilization is sufficiently free from raw material sulphur. In an oxidation reactor a fuel gas con¬ taining carbon monoxide and hydrogen is generated from the biological raw material using an oxygen containing gasifi¬ cation agent and part oxidation. A proportion of oxygen to biological material and a gas phase temperature is set and maintained in the oxidation reactor, guaranteeing fuel gas being nearly completely free from nitrogen oxide. A separa¬ tor removes suspended particles from the fuel gas siphoned from the oxidation reactor. The thus cleaned fuel gas is then converted into electric energy in fuel cells contain¬ ing a porous anode, a porous cathode and a carbonate melt electrolyte. Anode refers to the possibly catalytical ac¬ tive electrode of the fuel cell along which the fuel gas passes and where it is oxidized giving of electrons. Cath- ode refers to the possible catalytical active electrode or fuel cell being passed by a combustion agent being reduced by the uptake of electrons. For the conversion with oxygen to the carbonization at the cathode the combustion agent must contain carbon monoxide..Porous refers to an electrode structure which on one hand guarantees a contact of all three phases, fuel gas or combustion agent, electrode or catalyst and electrolyte, on the other hand, however, pre¬ vents the overflowing- of the electrolyte into the fuel gas chamber, or combustion agent gas chamber through capillary forces. The term porous relates therefor also to mesh structures with suitable mesh sizes. Fuel cells containing a carbonate melt electrolyte show a superior efficiency and high specific performance due to the comparatively high op¬ erating temperature. A further advantage of this type of fuel cell in connection with the generation of electricity from fuel gas formed from biological raw material is, that carbon monoxide, apart from not interfering with the ca¬ talysis can also like hydrogen, be used for the generation of electrical energy with carbon monoxide and carbonate ions reacting at the anode and a donation of electrons to carbon dioxide. On the whole, the combination results in a considerable synergy of electrical energy being generated with an especially high efficiency and reliability from a cheap and regenerative raw material with nearly no sulphur hydride, nitrogen oxide or particle emission. End products of this method are mainly harmless water and for the con- ventional energy generation unavoidable carbon dioxide. Furthermore heat is generated which especially in the use of the allothermal method can be recirculated into the process. With regards to another option of the invention the follow¬ ing method is employed: Biological raw material is used which for instance due to suitable fertilization is suffi¬ ciently free from raw material sulphur. In an oxidation re¬ actor a fuel gas containing carbon monoxide and hydrogen is generated from biological raw material and an oxygen con¬ taining gasification agent using part oxidation. In the oxidation reactor the proportion of oxygen to biological raw material and the gas phase temperature is set and main¬ tained, guaranteeing a near nitrogen oxide free fuel gas. A separator removes suspended particles from the fuel gas si¬ phoned from an oxidation reactor. The thus cleaned fuel gas is converted into electricity in fuel cells containing a porous anode, a porous cathode and an acidic electrolyte. This option contains in principle all characteristics and advantages of the carbonate melt electrolyte option. The fuel cell is, however, now operated at a comparatively low temperature. Overall the efficiency of an acidic electro¬ lyte is lower than. that of an carbonate melt electrolyte. This is, however, compensated by the fact that due to the comparatively low temperature, electrode corrosion can be controlled easier,. achieving extra reliability as for in- stance, fusion of the supporting frame of the electrode pore structure can definitely be avoided. Sulphuric acid or phosphoric acid are preferred electrolytes. Both acids and especially phosphoric acid show a relative high boiling point with little added water, so that fuel cells can be operated at high temperatures, i.e. 160°C. According to the method used by the invention different op¬ tions of part oxidation in the oxidation reactor can be oper¬ ated. Especially a direct part combustion of biological raw material can be carried out in ' the oxidation reactor. In one option, being of special significance, part oxidation is car¬ ried out with externally produced heat and a gasification agent containing mainly water vapour. In a different context this procedure is known as allothermal gasification. Al- lothermal gasification requires a supply of externally gener¬ ated heat as the conversion of biologically raw material with water vapour into fuel gas is altogether endothermic. The heat required for the part oxidation can preferably be pro¬ duced by combustion of biologically raw material or fuel gas. Preferably the heat for the part oxidation is being carried into the oxidation reactor by means of a usual heat transfer gas via a heat exchanger. In another option of the invention, part oxidation is carried out without the supply of exter¬ nally generated heat and with a gasification agent mainly containing water vapour and molecular oxygen or air. In an¬ other context this procedure is known as autothermal gasifi- cation. In this exothermal oxidation reactions are created by the molecular oxygen in the gasification agent creating "in- situ" heat for the endothermal reaction of water vapour and biological raw material. Autothermal or allothermal gasifica¬ tion is principally known from publication "Stahl und Eisen", issue 110, 1990 nr. 8, pages 131 to 136 although, however, in a different context. Another procedure within the concept of the invention for the generation of electrical energy from biological raw ma- terial features the following characteristics: Biological raw material is used which due to suitable fer¬ tilization is sufficiently free from raw material sulphur. In an oxidation reactor a carbon oxide and hydrogen con- taining fuel gas is generated from biological raw material with an oxygen containing gasification agent, using part oxidation. In the oxidation reactor a proportion of oxygen to biological raw material and a gas phase temperature, guaranteeing a near nitrogen oxide free fuel gas is set up and maintained. A separator removes suspended particles from the fuel gas syphoned from the oxidation reactor. The thus cleaned fuel gas is then converted into electrical en¬ ergy in a fuel cell containing a porous anode, a porous cathode and a solid metal oxide electrolyte, the fuel cell being operated at a minimum 800°C, again using autothermal or allothermal fuel generation. Because of the extreme operating temperature of fuel cells with solid metal oxide electrolyte, the catalytic effect of the electrodes is dispensable and a high reaction rate of the fuel gas on the anode and of the combustion agent on the cathode appears as the thermal energy of the gases lies considerably above the activation energy of the heteroge- nous dissociation reaction. High reaction rates in turn fa¬ cilitate a high specific electrical performance of fuel cells. Consequently preferred forms of fuel cells are oper- ated at a minimum of 1000°C and preferably at a minimum of 1200°C. Such . high operating temperatures can easily be set up if anode, cathode and electrolyte materials are coordi¬ nated or adapted with regards to their thermal expansion factors. It is understood that anode and cathode materials are also sufficiently corrosion resistant. The solid elec¬ trolyte can be set to a high ion conductivity if the elec¬ trolyte consists of a mixture of zirconium and calcium ox¬ ide or zirconium and yttrium oxide. A high ion conductivity combined with a high electrode reaction rate guarantees a high specific performance of the fuel cells. In a further form a ceramic metal preferably consisting of zirconium ox¬ ides and nickel or cobalt is preferably used as anode and LaNi0 3 or doping indium oxide as cathode material. To reduce possibly interfering carbon monoxide in fuel gas, the gas can be treated in a water shift reactor adding wa¬ ter vapour under increased temperatures to convert carbon monoxide to hydrogen and carbon dioxide. A possible inter¬ fering hydrocarbon content of the fuel gas can be reduced by passing the fuel gas directly before conversion to elec¬ trical energy through a reformer with a catalyst, prefera¬ bly with a transition metal catalyst and ideally with a nickel catalyst, the catalyst being operated at the same temperature level as the fuel cells. Below the invention is explained in detail according to a drawing showing just one example of the invention, in which: Fig.l represents a diagram of the Modular Power Plant of the invention and Fig. 2 a functional diagram .of Fig.l in relation to the gasification and fuel cell module. The Modular Power Plant shown in these drawings generates electrical energy from solar energy. The modular power plant consists of three special function modules: A conversion module 1 for the conversion of solar energy into biological raw material, being sufficiently free from raw material sulphur, in form of an agricultural area cul¬ tivated with plants, especially perennial C 4 -plants, being convertible into biological raw material. A gasification module 2 in form of a gasification reactor for the gasifi¬ cation of biological raw material into a fuel gas, using water vapour under heat and with the gasifiable products being contained in the gasification zone of the gasifica¬ tion reactor for a certain period, suppressing tar conden¬ sation in the zones following the gasification zone of the gasification module and/or in the follow-on fuel cell mod- ule. A fuel cell module 3 in which the fuel gas is con¬ verted into electrical energy. The conversion module 1 con¬ taining an aggregate 4 for the biological raw material har- vest and a processing aggregate 5 for the processing of biological raw material into a gasification preproduct. The processing aggregate can be stationary or mobile. The gasi¬ fication module 2 is connected to the processing aggregate 5 via a supply device 6. The fuel cell module 3 containing a fuel cell 7 is connected to the gasification module 2 by a device 8 for fuel gas cleaning. As part of the design the performance of the gasification module 2 and the fuel cell module 3 match, in relation to the system performance and are set in such a way that part of the fuel gas can be utilised for water vapour generation and a further part and/or the waste heat of the Modular Power Plant can be used for the drying of harvested biological raw material. The conversion module 1 contains a processing aggregate 5 for biological raw material in form of chaff cutter 9 or pelleter 10. The conversion module 1 also contains a stor¬ age facility 11 for the processed biological substance, compensating for quantity variations of processed biologi¬ cal raw material due to vegetation cycles. The principle elements of the conversion module 1, gasification module 2 and fuel cell module 3 can be transported assembled or dis¬ assembled and are normally prefabricated in a central loca¬ tion. Figure 2 shows the gasification module 2 being set for allothermal gasification. The gasification reactor 15 is principally designed for pressurised gasification using water vapour, the water vapour serving as gasification and fluidising agent. As mentioned above the fuel cell module 3 can contain various normally used fuel cells 7. Furthermore the example shows a water vapour module 12 connected via a line 13 being heated by part of the fuel gas by combustion. The waste heat can be utilised as described. Electrical energy can be tapped at position 14 of the Modu¬ lar Power Plant, used locally or fed into a net. Figure 2 shows the gasification reactor 15 with a device 16 for the supply of gasification preproducts and an ash pit 17 as part of the gasification model 2. Furthermore a heat exchanger 18 heats the water vapour. This heat exchanger 18 is heated by a gasification chamber 19, being supplied with part of the fuel gas. The water required for the water va- pour is supplied by a water treatment unit 20 and supplied to a steam generator 21. It is understood that pumps and valves are required and devices for waste heat utilisation are connected. The fuel cell module 3 operates with at least one of the described fuel cells 7, receiving the fuel gas, having been cleaned and freed from sulphur remnants. The gasification module 2 and the fuel cell module 3 are connected via an installation 22, a reactor 23 being of importance for in- creasing the hydrogen content of the fuel gas by a water gas process. Furthermore the unit comprises a heat ex¬ changer 24 and a quencher 25. The thus pretreated fuel gas enters the fuel cell 7 on the anode side which receives air via line 26 on the cathode side. In this respect Fig. 2 shows just one example.

Claims: Cl ims 1. A Modular Power Plant for the generation of electrical energy from solar energy, containing a) a conversion module for the conversion of solar en¬ ergy into biological raw material, being suffi¬ ciently free from raw material sulphur, in form of an agricultural area cultivated with plants, espe- cially C 4 -plants, being convertible to biological raw material, b) a gasification module in form of a gasification re¬ actor for the gasification of biological raw mate- rial into fuel gas, using water vapour, at in¬ creased temperatures, in which gasifiable products remain in the gasification zone of the gasification reactor for a certain period suppressing tar con¬ densation in the zones after the gasification zone of the gasification module and/or in a subsequent module, c) a fuel cell module in which fuel cell gas is con¬ verted into electricity using fuel cell technology, in which the conversion module contains an aggregate for harvesting biological raw material and a processing ag¬ gregate for processing biological raw material to a gasi¬ fication preproduct, the gasification module being con- nected to the processing aggregate by means of a supply unit, the fuel cell module being connected to the gasifi¬ cation module for cleaning of the fuel gas by a device, the performance of the gasification and fuel cell module matching and being set in relation to the system perform¬ ance and in such a way, that part of the fuel gas can be utilised for water vapour generation and a further part and/or waste heat of the Modular Power Plant can be used for the drying of harvested biological raw material, the size of the conversion module depending on the stipulated and system performance in relation to the cultivated area, the conversion module containing a processing ag¬ gregate in form of at least one harvester for biological raw material, and a chaff cutter or pelleter and princi¬ ple elements of the conversion, gasification and fuel cell module being prefabricated as modular elements of a Modular Power Plant and being transportable in an assem- bled and disassembled condition. 2. A Modular Power Plant according to claim 1, charac¬ terised by the gasification module being set for allothermal gasification. 3. A Modular Power Plant according to claim 1 or 2, characterised by the gasification module contain¬ ing at least one gasification reactor operating under pressure with water vapour as gasification and fluidis- ing agent (EP 0 329 673 Bl) . 4. A Modular Power Plant according to claims 1 to 3, characterised by the gasification module being set to an oxygen to biological raw material proportion and gas phase temperature guaranteeing a virtual nitro¬ gen oxide free fuel gas. A Modular Power Plant according to claims 1 to 4, characterised by the fuel cell module containing at least one fuel cell with a phosphor acidic electro¬ lyte. A Modular Power Plant according to claims 1 to 4, characterised by the fuel cell module containing at least one fuel cell with a carbonate melt electro¬ lyte. A Modular Power Plant according to claims 1-4, char¬ acterised by the fuel cell module containing at least one solid oxide fuel cell. 8. A Modular Power Plant according to claims 1-4, char¬ acterised by the fuel cell module containing at least one proton exchange membrane fuel cell. 9. A Modular Power Plant according to claims 1 to 8, characterised by a combination of fuel cells ac¬ cording to claims 5 and/or 6 and/or 7 and/or 8. - 10. A Modular Power Plant according to claims 1 to 9, characterised by an additional water vapour od- ule being heated by part of the fuel gas.

Inventors: BINSMAIER HANNELORE, JOHNSSEN WOLF, BINSMAIER, HANNELORE, JOHNSSEN, WOLF
Applicants: BINSMAIER HANNELORE, JOHNSSEN WOLF, BINSMAIER, HANNELORE, JOHNSSEN, WOLF
Application year: 1994
Main classification: H01M8
IPC codes: H01M8